These are commonly referred to as tool check tags or miners tags. The idea being when you brought out a cart from a mine, you put a tag on a board so you would get paid for a load. Tool check in that when you took out a bucket of tools, you placed your tag on the board to keep track of who had the tools.
Like you, I also have suspicions that they were used on livestock as well. I hunt primarily 1850 - 1900 farmhouses and find them by pocketful. Although, yours DOES have a nice design around the edge.